The present invention relates to a gas laser oscillator low in fluctuation rate of laser beam, capable of producing laser beam stably, and free from malfunction.
First, a conventional gas laser oscillator is described by referring to FIG. 11. In FIG. 11, reference numeral 1 is a discharge tube for forming a discharge space 5 inside, and the inside of the discharge tube 1 is filled with laser gas, or laser gas is circulating by a circulating device not shown in the drawing. Reference numeral 2 is an electrode provided at one end of the discharge tube 1, 3 is an electrode provided at other end of the discharge tube 1, 4 is a direct-current high voltage power source for applying a voltage for discharging between the electrodes 2 and 3, and 6 is a fully reflective mirror, which is combined with a partially reflective mirror 7 to compose an optical resonator for amplifying the laser light. Reference numeral 9 is an output control device for controlling the direct-current high voltage power source 4.
This is the basic constitution of the gas laser oscillator. In thus constituted gas laser oscillator, the operation of its basic portion is described below. First, according to the command from the output control device 9, a direct-current high voltage in pulse form is applied between the electrodes 2 and 3 from the direct-current high voltage power source 4 for discharging between the electrodes 2 and 3. By this discharge energy, the laser gas in the discharge space 5 is excited. The excited laser gas is set in resonant state by the optical resonator composed of the fully reflective mirror 6 and partially reflective mirror 7, and the light is amplified, and a laser beam 8 is issued from the partially reflective mirror 7. The produced laser beam 8 is used in laser processing such as cutting and piercing.
In such gas laser oscillator, also on standby while not processing, discharge occurs in the discharge tube 1, and the laser beam 8 is issued from the partially reflective mirror 7 at a preset output level. However, since an absorber 10 is disposed ahead of the partially reflective mirror 7, the produced laser beam 8 is intercepted by the absorber 10 and does not leak outside.
When processing by the laser beam 8, by the command from an absorber control device 12, an absorber drive device 11 operates the absorber 10, and the passage of laser beam 8 is opened, and the laser beam 8 is emitted outside to process the workpiece 15.
On the other hand, at the side closer to the workpiece 15 from the absorber 10 on the optical axis of the laser beam 8, a beam splitter 14 is disposed. The laser beam 8 is separated by this beam splitter 14, and the straightforward portion 8a reaches the workpiece 15, and processes by cutting or piercing. The portion 8b reflected and separated by the beam splitter 14 is focused by a focusing lens 16, and irradiates a detector 17. The detector 17 irradiated by the separated portion 8b detects that the laser beam 8 is being emitted. This detection signal is amplified by an amplifier 18, and is issued from a terminal 19.
However, the conventional gas laser oscillator as explained above had several problems.
First was a problem of fluctuation of laser beam output in a transient state from standby by cutting off the laser beam 8 by the absorber 10 to processing by passing the laser beam 8 by setting aside the absorber 10. That is, in the standby state (A) as shown in FIG. 7, a signal for obtaining an output of low level necessary for maintaining discharge is issued from the output control device 9, and a direct-current high voltage corresponding to the signal level is applied between the electrodes 2 and 3 to maintain discharge. Once a processing start signal is entered and the absorber 10 is opened to be in state (B), the processing start signal 13 is sent from the absorber control device 12 into the output control device 9. Receiving this signal 13, the output control device sends out a signal having level and waveform necessary for obtaining the output of pulse laser beam 8 suited to the purpose of processing. In the conventional control, however, since the discharge state in the discharge space 5 on standby is different from the discharge state in the discharge space 5 during processing, the dissociation state of laser gas is different between processing and standby. It hence takes time until the dissociation state of laser gas is stabilized from start of processing and fluctuations of laser output in the initial period of processing are large so that stable processing is disabled. Upon start of processing, further, it takes time to stabilize owing to the presence of unstable period due to heat effects of the fully reflective mirror 6 and partially reflective mirror 7 for composing the optical resonator and unstable period of surface state of the electrode 2 and electrode 3, which is also a cause of unstable output of the laser beam 8 in the initial period of processing. This unstable output of the laser beam 8 in the initial period of processing was a serious problem in processing for a short time, in particular.
Other problem is related to the laser beam detecting device that is indispensable for accurate control of the gas laser oscillator. In the conventional constitution shown in FIG. 11, after dismounting the beam splitter 14 for the purpose of adjustment of gas laser oscillator or the like, if laser processing is done without reassembling the beam splitter 14, the laser beam 8 not attenuated by the beam splitter 14 directly irradiates to the workpiece 15. As a result, the workpiece is irradiated with an exessive laser beam 8, and processing failure may occur.
Or, when adjusting the gas laser oscillator, if a laser beam 8 over the allowable capacity of the detector 17 is irradiated by mistake, the detector 17 may be broken.
Further, the detector 17 may fluctuate in the detecting sensitivity due to fluctuations of temperature depending on heat generation by incident of laser beam 8b or ambient temperature. Fluctuation of detecting sensitivity of the detector 17 may cause output of wrong information. For example, if the detecting sensitivity is raised, although laser beam 8 is not emitted, it may be falsely recognized that the laser beam 8 is emitted, or if the detecting sensitivity is lowered, although the laser beam is emitted, it may be falsely recognized that the laser beam 8 is not emitted. Hence, accurate control of the gas laser oscillator may be disabled.
Still more, if used for a long period, dust may deposit on the beam splitter 14, focusing lens 16, or detecting surface of the detector 17, and the detecting sensitivity may be lowered.